As verbs the difference between keep and diff
is that
keep is to continue in (a course or mode of action); not to intermit or fall from; to maintain while
diff is (computing) to run a diff program on (files or items) so as to produce a description of the differences between them, as for a patch file.
As nouns the difference between keep and diff
is that
keep is (obsolete) care, notice while
diff is (slang).
As a proper noun diff is
(computing) a program, historically part of the unix operating system, which compares two files or sets of files and outputs a description of the differences between them.